| An instance of a TransactionResourceImpl is a bundle of things that
connects a connection to the database - it is the transaction "context" in
a generic sense. It is also the object of synchronization used by the
connection object to make sure only one thread is accessing the underlying
transaction and context.
TransactionResourceImpl not only serves as a transaction "context", it
also takes care of:
- context management: the pushing and popping of the context manager in
and out of the global context service
- transaction demarcation: all calls to commit/abort/prepare/close a
transaction must route thru the transaction resource.
- error handling
The only connection that have access to the TransactionResource is the
root connection, all other nested connections (called proxyConnection)
accesses the TransactionResource via the root connection. The root
connection may be a plain EmbedConnection, or a DetachableConnection (in
case of a XATransaction). A nested connection must be a ProxyConnection.
A proxyConnection is not detachable and can itself be a XA connection -
although an XATransaction may start nested local (proxy) connections.
this is an example of how all the objects in this package relate to each
other. In this example, the connection is nested 3 deep.
DetachableConnection.
lcc cm database jdbcDriver
^ ^ ^ ^
| | | |
|======================|
| TransactionResource |
|======================|
^ |
| |
| | |---------------rootConnection----------|
| | | |
| | |- rootConnection-| |
| | | | |
| V V | |
|========================| |=================| |=================|
| EmbedConnection | | EmbedConnection | | EmbedConnection |
| |<-----| |<-----| |
| (DetachableConnection) | | ProxyConnection | | ProxyConnection |
|========================| |=================| |=================|
^ | ^ ^ ^
| | | | |
---rootConnection-- | | |
| | |
| | |
|======================| |======================| |======================|
| ConnectionChild | | ConnectionChild | | ConnectionChild |
| | | | | |
| (EmbedStatement) | | (EmbedResultSet) | | (...) |
|======================| |======================| |======================|
A plain local connection must be attached (doubly linked with) to a
TransactionResource at all times. A detachable connection can be without a
TransactionResource, and a TransactionResource for an XATransaction
(called XATransactionResource) can be without a connection.
| 